1. Field of Invention
The present invention relates to a variable compression ratio (VCR) apparatus, and more particularly, to a VCR apparatus with dual eccentric links.
2. Description of Related Art
In general, the thermal efficiency of an engine increases when a compression ratio is high. In the case of a spark ignition engine, when ignition timing is advanced to a predetermined level, the thermal efficiency thereof increases.
In the spark ignition engine, however, when the ignition timing is advanced at a high compression ratio, abnormal combustion may occur to damage the engine. Therefore, there is a limit to advancing the ignition timing, and thus a power reduction inevitably occurs.
A VCR apparatus refers to an apparatus for changing a compression ratio of a fuel-air mixture according to an operation state of an engine.
The VCR apparatus increases the compression ratio of the fuel-air mixture to improve fuel efficiency, at a low load condition of the engine. Furthermore, the VCR apparatus reduces the compression ratio of the fuel-air mixture to prevent the occurrence of knocking and improve the engine power, at a high load condition of the engine.
The VCR apparatus according to the related art includes a connecting rod connected to a piston and receiving combustion power of the fuel-air mixture, a pin link receiving the combustion power of the fuel-air mixture from the connecting rod and rotating a crank shaft, and a controller changing a rotating trace of the pin link according to an operation condition of the engine.
In the VCR apparatus according to the related art, the compression ratio of the fuel-air mixture is changed as the rotating trace of the pin link is changed.
FIG. 1 illustrates a VCR apparatus for changing a compression ratio as described above, which has been disclosed in U.S. Pat. No. 6,581,552. Referring to FIG. 1, an eccentric member 3 is swung with respect to one side surface of a connecting rod 1 by an eccentric control link 2, and an eccentric ring 3a formed at a small end portion 1a of the connecting rod 1 is eccentrically formed. Accordingly, a piston pin coupled to the eccentric ring 3a varies the height of the piston pin through the control of the eccentric member 3, thereby changing a compression ratio.
In the VCR apparatus according to the above-mentioned patent, a guide member 4 is formed on one side surface of eccentric member 3, and a guide groove is coupled to connecting rod 1 so as to correspond to guide member 4. That is, since the VCR apparatus has a cantilever structure in which guide member 4 is formed, the VCR apparatus has a problem in that torsion occurs in a vertical direction with respect to the center of a rotating shaft, during the rotation about the eccentric ring 3a. 
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.